Technical 14 www.aftermarketonline.net DECEMBER/JANUARY 2026 Oils well that ends well if you know your filter tech Filtration expert UFI says understanding how the lifecycle of oil filters can impact vehicles is vital know-how for technicians Why does the oil filter, an apparently ordinary component, become the ‘main character’ whenever maintenance is carried out and how do thousands of driving miles affect it? 0km: Brand new In a newly replaced oil filter, the structure of the filter paper and the internal components are in the same condition as when they left the production line. Inside, there is a nonreturn valve, whose function is to prevent oil from draining out of the filter when the engine is switched off, ensuring a perfect seal. The bypass valve only operates during cold starts, while under normal conditions it remains closed. When oil passes through the filter, any mechanical impurities and colloids inside can be effectively removed. The oil flows easily through the filtering media, encountering low resistance. This means it reaches components such as the crankshaft and camshaft surfaces precisely, forming a complete film. This creates a contaminant-free lubricating environment for the engine, thereby preventing premature wear of its internal parts. 0-30,000km: Highefficiency operation As the vehicle’s mileage increases, in the oil filter the surface of the filtering media gradually traps impurities such as metal fragments and colloids. During this process, due to the constant absorption of these particles, the filtration pores gradually become blocked. However, filtration efficiency actually ‘improves’ until it reaches peak performance. At this stage, the filter can effectively remove impurities from the oil. The bypass valve remains ‘inactive’, and the oil flow resistance slowly increases while remaining within a safe and controllable range. Over 30,000km: Critical period for failures With further mileage, the filtration precision of the oil filter drops significantly. At this stage, the filter media accumulates a large number of impurities, and oil flow resistance increases considerably. The bypass valve starts to activate occasionally, allowing unfiltered oil to flow directly into the engine, causing serious wear to its internal components. With prolonged use, the non-return valve tends to lose its elasticity, reducing its hydraulic seal. This phenomenon causes oil to return to the sump. When starting the engine, the oil hydraulic circuit also takes longer to reach operating pressure, leading to non-continuous or delayed lubrication of parts. This
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